Electric heating and forming apparatus



y 27, 1943- w. E. CRAWFORD 2,325,479

ELECTRIC HEATING AND FORMING APPARATUS Filed June 5, 1941 William E. Crawfam INVENTOR.

ATTORNEY Patented July 27, 1943 ELECTRIC HEATING AND FORMING APPARATUS William E. Crawford, Wanwatosa, Win, assignor s to A. 0. Smith Corporation, Milwaukee, Win, a 1

corporation of New York Application June 5, 1941, Serial No. 396,688

' 1: Claims.

This invention relates to electric heating and forming apparatus and more particularly to an improvement in heating and forming apparatus such as that set forth in the co-pending application of Warren F. Heineman, Serial No. 391,234, filed May 1, 1941, and assigned to a common assignee herewith.

The object of the present invention is to more adequately control the heating of the article being formed.

One embodiment of the invention is illustrated in the accompanying drawing in which:

Figure 1 is a longitudinal central section through the electrode dies and current choke;

Fig. 2 is a transverse section through the apparatus on line 2-2 of Fig. 1; and

Fig. 3 is a transverse section on line 3-3 of Fig. 1.

In the preferred embodiment illustrated the forging dies comprise three die segments I, 2 and 3, arranged in a circle to provide a complemental die recess for receiving a pipe 4 or other article and forging the end thereof. The shape of the die recess may vary depending upon the shape to be given to the finished article, that illustrated being for the purpose of nosing down and upsetting the end of the pipe as in the manufacture of bombs or of air bottles and the like.

The die segments are circumferentially sepa-' rated from one another and the spaces between their respective edges are filled with a refractory insulating material 5 for electrically insulating the segments from one another.

The heating current is supplied to the segments through three transformers 8, I, and 8 which have their primaries connected between the respective leads 9, I0 and I I of a three phase alternating current source. The secondaries of the three transformers are connected by separate pairs of leads I2, I3 and I4, to opposed edges of the segments I, 2 and 3 respectively. The leads I2, I3 and I4 are connected to the die segments at the forward ends of the latter in order to facilitate the application of the heaviest heating currents at the location where pipe 6 first engages the dies, to more rapidly heat the pipe at this position. a

In the forming operation the pipe 4 is rotated relative to the dies and is pushed into the die cavity where it engages the separate segments and further movement effects an upsetting of the softened metal.

Heretofore certain difilculties have arisen in the operation of a machine of the type above described. In the manufacture of bomb bodies, for instance, it has been found that the current tends to travel toward the closed end of the die through the segments and to pass through the article at a position near its end. This tendency causes excessive heating of the article at its end during the latter stages of the forming operation and the metal may become so soft as to fail to maintain its shape or the desired pressure contact with the dies. If the metal at the outer surface of the article becomes molten it may injure the dies and cause additional prob lems of inaccuracy in shape of the article.

The present invention is directed primarily to overcoming this difficulty, and in accordance with the invention, the longitudinal fiow of heating current toward the closed end of the die is opposed or choked. This is preferably accomplished by inserting laminations II of magnetically permeable materia1 in the gaps between the electrode segments to the rear of leads I2, I3 and II.

The inner edges of laminations It should be shaped to generally correspond to the shape of the die cavity, although it is not necessary that the laminations actually form a part of the die surface since their edges are preferably protected by suitable refractory material II. The

v laminations it are insulated from the segments {1,12 and 3 so as not to conduct electricity between In some instances the gap between the segments I, 2 and 3 may be widened to the rear of leads I2, I3 and I4. This may increase the resistance of the current path sufiiciently to reduce the diversion of current through the nose of the article, and the wider gap may serve to provide for more laminations I8 which will in- -crease the choking effect on the current being diverted. In other instances, it may be desirable to have a wider gap at the forward or larger end of the dies to provide a longer current path through the article at this point and consequently greater heating, and in this case the laminations it may be employed to desirably limit the diversion of current to the rear end ofthe electrodes.

Another feature of the present invention lies in providing an end piece I8 which holds the plug I5 and which constitutes a substantial part of the end surface of the die cavity. The piece I B is insulated from the segments I, 2 and 3 and preferably carries no current. Suitable water cooling means I 9 may be provided in piece I8 and in the rear end of the die segments to additionally control-the heating of the article as it moves into the die.

The die segments are held in place by end rings 20 and 2i which are insulated from them, and which are secured to them by insulated bolts 22. The end rings have inturned flanges 28 and 24, respectively, extending into a recess in the die segments or over the outer surface of the segments to hold them against outward pressure from the article being formed and to relieve the bolts 22 of stress.

While the invention has been shown as applied to three electrodes supplied by a three phase current-source, it will beunderstood that it may be applied to a machine having only-two electrodes or to one employing any plural number of electrodes.

The invention may have various embodiments within the scope or the claims.

I claim:

1. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, means to pass a heating current through the portion of the article contacting with said 'segments as the article and die are rotated relative to one another, and means to control the temperature of the article independently in difierent longitudinal regions of the die.

2. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially and insulated from one another, means connecting said die segments at the larger end of the die cavity to the respective terminals or a source of heating current, and means atthe smaller end of the die cavity for preventing excessive heating of the article in this region.

3. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially and insulated from one another, means connecting said die segments at the larger end of the die cavity to the respective terminals of a source of heating current, and means at the smaller end of the die cavity for cooling the article- 4. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially, means connecting said die segments at the larger end of the die cavity to the respective terminals of a source of heating current, and an end piece closing the rea end of the die cavity and insulated from said segments to prevent the passage of heating current to the article at the rear end of the die cavity. I

5. In an electric heating and forming apparatus, a pluralityof die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially, and means connecting said die segments at the larger end of the die cavity to the respective terminals of a source of heating current, the spaces between the electrode die segments being greater in certain regions to provide for increased resistance to the flow of heating current through the article in such regions.

6. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially,

creasing the resistance of the current path in.

difierent longitudinal regions 01' the die segments.

8. In anelectric heating and forming apparatus, a pluralltyof die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially, means connecting said die segments at the larger end of the die cavity to the respective terminals of a source of heating current, and means limiting the flow of current to the article in different longitudinal regions of the die segments.

9. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments beingspaced apart circumierentially, means connecting said die segments at the larger end of the die cavity to the respective terminals of a source of heating current, and a magnetic reactance member disposed between the edges of the die segments to the rear of said connecting means.

10. In an electric heating and forming apparatus, a pluraltiy of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumierentially, means connecting said die segments at the larger endof the die cavity to the respective terminals of a source of heating current, and a laminated magnetic member disposed between the edges of the die segments to the rear of said connecting means and insulated from said segments.

11. In an electric heating and forming apparatus, a plurality of circumferentially spaced die segments defining a die cavity for receiving and forming an article, said segments being insulated from one another, electrical connections for supplying current to said segments in one longitudinal region thereof, and means for preventing the fiow of such current to other longitudinal regions of said segments.

12. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receivingand forming an article, said segtments being spaced apart circumferentially and insulated from one another, electrical connections for supplying current to said segments in one longitudinal region thereof, and a magnetic impedance limiting the fiow of such current to other longitudinal regions of said segments.

13. In an electric heating and forming apparatus, a plurality of die segments defining a die cavity for receiving and forming an article, said segments being spaced apart circumferentially and providing electrodes for applying a heating current to the article, a ring at the end thereof, and means securing said segments to said ring to hold the segments in place, said ring being insulated from said segments.

WILLIAM E. CRAWFORD. 

